I would like to offer a suggestion for the caller (Bruce) who had a tire that appeared to be fine most of the time, but then seemed to lose a large amount of air overnight. I had something similar happen. After many months, several trips to different mechanics, and being told that there was no leak, I finally concluded that it might be the rim. My thought was that the leak might occur only when the wheel (and rim) were stopped in a certain position. I ordered a new rim from the dealer, and to the surprise of the mechanics who installed it, my old one had a hairline crack that was clearly visible with the tire removed. Replacing the rim fixed the problem for good. The same thing may be happening to the listener, or if he’s never had his tire checked, there may be an object in the tire that causes a leak only when the wheel is stopped in a certain position. I believe Ray suggested the latter possibility.
An excellent suggestion tkitt.
I’ll add that hairline fractures can be readily detected with a liquid called “dye penetrant”. It cavitates into fractures that are invisable to the naked eye and highlights them.
There are other nondestructive techniques, but dye pen is easy and cheap.
And yes, the wheel should be nondestructively inspected. A hairline fracture can instantly fail catastrophocally and result in a serious accident.